270 MR. F, BALFOUR-BROWNE ON THE [Mar. 2, 
find the average number of days occupied by each stage, and the 
results, so far as it is possible to get any, are as follows :— 
TABLE 2. 
arya Number Max. Min. 
Stage 5 of number of | number of 
number of days. nymphs. days. days. 
Vv. 9°5 6 ia t 
VI. 15 8 31 9 
VII. 12°0 14 22 6 
VIII. 133 13 23 5 
IX. 14-1 12 21 8 
Xe 19°2 10 AT + 9) 
Nal 29°44 5 52+ | 10 ; 
The figures indicate that the stages tend to lengthen from the 
earlier to the later ones. There is, however, a source of error in 
the method used, and that is that while some nymphs are full- 
grown at the end of the tenth stage, others go through 11, 12, 13, 
or 14 stages. Now one point which is quite clear without any 
statistics is that the final stage is always a fairly long one, and 
this fact will of course affect the above figures. I have therefore 
checked these results by using Table 1 in another way. I have 
taken the average duration of the last stage of each nymph, then 
of the penultimate stage, then of the one before that, and so on as 
far back as my figures will permit, again of course only including 
stages begun and completed in the incubator, and the results are 
as follows :— 
TABLE 3. 
| | Penultimate Last 
: Stage. Stage. 
Successive i A ee 2 
stages ; 4—8 5—9 6—10 7—11 8—12 | 9—13 10—14. 
Number of ; | 
nymphs } 4, 11 14, 15 iL 6 3 
Average no. 12°3 10°7 13°4 147 | 168 19°5 456+ 
of days | 
Max. & min. 2 | / / i 4 FS 8 
no. of days $ ly, 10, 22, 8 |) Sil, &, | 44. 6. | 24. 9. 24, 14. 62+ 36. 
Again the figures show that the stages tend to lengthen out as 
the nymph grows bigger. 
The first imago to appear emerged 33 weeks (230 days) after 
hatching from the egg and after passing through 10 stages. This 
was one of the individuals which spent the winter in the incubator, 
and I expected to find that all the nymphs which had been kept 
warm during winter and had fed and moulted regularly would 
complete their life in the same number of stages. However, out 
of ten such nymphs only three got through in 10 stages, one in 11, 
five in 12,and one in 14. The three nymphs which completed in 
10 stages were placed in the incubator in their 4th stage, aS was 
